Wafer inspection system, wafer inspection apparatus and prober

ABSTRACT

A wafer inspection system is provided. The wafer inspection system includes: a transfer region in which a transfer device is arranged; an inspection region in which test heads for inspecting a substrate are arranged; and a maintenance region in which the test heads are maintained. The inspection region is located between the transfer region and the maintenance region, a plurality of inspection rooms accommodating the test heads are adjacent to each other in the inspection region, and the test heads are configured to be unloaded from the inspection region to the maintenance region.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.16/671,410, filed on Nov. 1, 2019, which is a continuation of U.S.patent application Ser. No. 15/582,848, now issued as U.S. Pat. No.10,753,972, filed on May 1, 2017, and a continuation of U.S. patentapplication Ser. No. 14/525,431, now issued as U.S. Pat. No. 9,671,459,filed on Oct. 28, 2014, which claims the benefit of Japanese PatentApplication No. 2013-224460, filed on Oct. 29, 2013, the entiredisclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The embodiments described herein pertain generally to a wafer inspectionsystem, a wafer inspection apparatus and a prober.

BACKGROUND

There has been used a prober as a wafer inspection apparatus to performan electrical characteristic test on each of multiple semiconductordevices formed on a semiconductor wafer (hereinafter, simply referred toas “wafer”). The prober includes a probe card facing the wafer, and theprobe card includes multiple contact probes as a multiple number ofcolumn-shaped contact terminals (see, for example, Patent Document 1).In this prober, a test signal is outputted to a semiconductor deviceconnected to an electrode pad or a solder bump through each of thecontact probes of the probe card, so that a conducting state of anelectrical circuit of the semiconductor devices can be inspected.

A test signal is sent to each of the contact probes of the probe cardfrom a test head having a main board as a test circuit. Recently, inorder to improve wafer test efficiency, there has been developed a waferinspection apparatus which includes multiple test heads each having aprobe card and inspects a semiconductor device of a wafer with a singletest head while the wafer is transferred to another test head. In thiswafer inspection apparatus, from the viewpoint of reduction infootprint, cells each accommodating multiple test heads are stacked atmultiple levels.

Since a main board of each test head is a kind of consumables, the mainboard needs to be regularly replaced. In order to replace the mainboard, the test head needs to be unloaded from the wafer inspectionapparatus to above a maintenance carriage.

-   Patent Document 1: Japanese Patent Laid-open Publication No.    2012-063227

However, the test head has a weight of about 70 kgf and is supported bya slide rail. Thus, it is difficult to move the test head in otherdirections than in an unloading direction. Therefore, it is necessary tocorrectly adjust a position of the maintenance carriage to a position ofthe test head. However, since the maintenance carriage includes a liftdevice or the like and has a high weight, it is difficult to finecontrol the position thereof. As a result, it is difficult to unload thetest head.

SUMMARY

In view of the foregoing, example embodiments provide a maintenancecarriage for a wafer inspection apparatus capable of easily unloading atest head and a maintenance method for the wafer inspection apparatus.

In one example embodiment, a wafer inspection system is provided. Thewafer inspection system comprises: a transfer region in which a transferdevice is arranged; an inspection region in which test heads forinspecting a substrate are arranged; and a maintenance region in whichthe test heads are maintained. The inspection region is located betweenthe transfer region and the maintenance region, a plurality ofinspection rooms accommodating the test heads are adjacent to each otherin the inspection region, and the test heads are configured to beunloaded from the inspection region to the maintenance region.

A maintenance carriage which is movable and is configured to support theunloaded test heads may be arranged in the maintenance region. Themaintenance carriage may be configured to accommodate the test heads andhas a case which is movable up and down, and the case may be allowed todirectly face one of the inspection rooms by moving the maintenancecarriage and by moving the case up and down.

A position of the maintenance carriage and a position of the case may beconfigured to be fixed. A guide rail configured to control a movingdirection of the maintenance carriage may be arranged in the inspectionregion. Each of the plurality of inspection rooms may have an openingfacing the maintenance region, and each of the test heads may beconfigured to be unloaded to the maintenance region via the opening.

In another example embodiment, a wafer inspection apparatus is provided.The wafer inspection apparatus comprises: a plurality of inspectionrooms comprising test heads to be maintained for inspecting a substrateon which a semiconductor device is formed and a guide rail for unloadingthe test heads to be maintained to a maintenance region; and a loaderconfigured to transfer the substrate into one of the inspection rooms.The plurality of inspection rooms are arranged at a cell tower betweenthe loader and the maintenance region, and the loader and themaintenance region are arranged at opposite sides of the cell tower.

In another example embodiment, a wafer inspection apparatus is provided.The wafer inspection apparatus comprises: a plurality of inspectionrooms comprising test heads to be maintained for inspecting a substrateon which a semiconductor device is formed and a guide rail for unloadingthe test heads to be maintained to a maintenance region; and a loaderconfigured to transfer the substrate into one of the inspection rooms.The plurality of inspection rooms are arranged between the loader andthe maintenance region, and the loader and the maintenance region arefacing to each other across the plurality of inspection rooms.

In another example embodiment, there is provided a prober for inspectingelectrical characteristics of a semiconductor device formed on asubstrate. The prober comprises: a probe card facing the substrate andhaving a plurality of probes; test heads arranged at an opposite side ofthe substrate with respect to the probe card; a lifting deviceconfigured to move the test heads up and down in a vertical direction;and a guide rail configured to unload the test heads in a directionperpendicular to the vertical direction.

In accordance with the example embodiments, after a position of thecarriage base is fixed and the case is moved up to a position of thetest head to be maintained to be fixed, the position of the case can befine controlled in the horizontal direction. Therefore, the case candirectly face the test head to be maintained. As a result, it ispossible to easily unload the test head toward the case.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description that follows, embodiments are described asillustrations only since various changes and modifications will becomeapparent to those skilled in the art from the following detaileddescription. The use of the same reference numbers in different figuresindicates similar or identical items.

FIG. 1 is a perspective view schematically showing a configuration of awafer inspection apparatus to which a maintenance carriage is applied inaccordance with an example embodiment;

FIG. 2A and FIG. 2B show components included in each cell of a celltower of FIG. 1, and to be specific, FIG. 2A is a perspective view of atest head, and FIG. 2B is a front view illustrating an arrangement ofthe test head, a pogo frame, and a probe card in each cell;

FIG. 3A and FIG. 3B schematically illustrate a configuration of themaintenance carriage in accordance with the present example embodiment,and to be specific, FIG. 3A is a side view thereof, and FIG. 3B is afront view thereof;

FIG. 4A and FIG. 4B schematically illustrate configurations of a lifterand a test head case of FIG. 3A and FIG. 3B, and to be specific, FIG. 4Ais a side view thereof, and FIG. 4B is a front view thereof;

FIG. 5 is a partially enlarged view showing a movable fit between aguide unit and a guide rail;

FIG. 6A and FIG. 6B are side views schematically illustrating aconfiguration of a simple maintenance carriage, and to be specific, FIG.6A illustrates a case where maintenance is conducted on a test head of afirst-level cell in the cell tower, and FIG. 6B illustrates a case wheremaintenance is conducted on a test head of a second-level cell in thecell tower;

FIG. 7A to FIG. 7C are process diagrams for explaining a maintenancemethod for a wafer inspection apparatus with the maintenance carriage ofFIG. 3A and FIG. 3B; and

FIG. 8 is a front view illustrating a modification example ofarrangement of the maintenance carriage of FIG. 3A and FIG. 3B.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of the description. In thedrawings, similar symbols typically identify similar components, unlesscontext dictates otherwise. Furthermore, unless otherwise noted, thedescription of each successive drawing may reference features from oneor more of the previous drawings to provide clearer context and a moresubstantive explanation of the current example embodiment. Still, theexample embodiments described in the detailed description, drawings, andclaims are not meant to be limiting. Other embodiments may be utilized,and other changes may be made, without departing from the spirit orscope of the subject matter presented herein. It will be readilyunderstood that the aspects of the present disclosure, as generallydescribed herein and illustrated in the drawings, may be arranged,substituted, combined, separated, and designed in a wide variety ofdifferent configurations, all of which are explicitly contemplatedherein.

A maintenance carriage for a wafer inspection apparatus in accordancewith the present example embodiment will be explained first.

FIG. 1 is a perspective view schematically showing a configuration of awafer inspection apparatus to which a maintenance carriage is applied inaccordance with the example embodiment.

A wafer inspection apparatus 10 of FIG. 1 includes a cell tower 12 inwhich multiple inspection rooms (cells) 11 are arranged at multiplelevels, for example, at four levels; and a loader 13 which is arrangedto be adjacent to the cell tower 12 and configured to load and unloadwafers with respect to respective cells 11 with a transfer device (notillustrated) provided therein. Each of the cell tower 12 and the loader13 has a rectangular parallelepiped having a height of, for example, 2.4m.

In the wafer inspection apparatus 10, at an opposite side (hereinafter,referred to as “outside”) to a surface of the cell tower 12 adjacent tothe loader 13, a space available for maintenance of each cell 11 by anoperator is secured, and a maintenance carriage 27 to be described lateris arranged therein.

FIG. 2A and FIG. 2B show components included in each cell of the celltower of FIG. 1, and to be specific, FIG. 2A is a perspective view of atest head, and FIG. 2B is a front view illustrating an arrangement ofthe test head, a pogo frame, and a probe card in each cell.

A test head 15 depicted in FIG. 2A includes a main body 16 formed of arectangular parallelepiped housing and a flange 17 protruding from anupper portion of a side surface of the main body 16 in a longitudinaldirection thereof toward the side direction thereof. The main body 16accommodates a main board (not illustrated) as a test circuit.

Further, as depicted in FIG. 2B, in each cell 11, the test head 15, aprobe card 18, and a pogo frame 19 configured to support a pogo pin (notillustrated) electrically connecting the probe card 18 and the mainboard are provided. Sealing members 20 and 21 are arranged between theprobe card 18 and the pogo frame 19 and between the pogo frame 19 andthe test head 15, respectively. Since spaces surrounded by the sealingmembers 20 and 21 are depressurized, the probe card 18 and the pogoframe 19 are vacuum-attracted and attached to the test head 15.

The probe card 18 includes a circular plate-shaped main body 24 andmultiple contact probes 25 as a multiple number of column-shaped contactterminals arranged to protrude from a lower surface of the main body 24toward a lower side in the drawing. When a wafer (not illustrated) isbrought into contact with the probe card 18, each of the contact probes25 is brought into contact with an electrode pad or a solder bump (notillustrated) of each semiconductor device formed on the wafer.

Returning back to FIG. 1, a maintenance opening 26 is formed the outsideof each cell 11, and the test head 15 is unloaded through thismaintenance opening 26. The operator may unload a used main board fromthe unloaded test head 15 and provide a new main board to the test head15.

Since the test head 15 has a weight of about 70 kgf, it is difficult forthe operator alone to handle the test head 15. Therefore, the test head15 is supported via the flange 17 by a slide rail (not illustrated)provided along a longitudinal direction of the test head 15(hereinafter, simply referred to as “longitudinal direction”) within thecell 11 and unloaded in the longitudinal direction by multiple ballsprovided on an upper surface of the slide rail.

In order for the operator to easily replace a main board in the waferinspection apparatus 10, a supporting device to support the unloadedtest head 15 is needed. Therefore, as the supporting device, themaintenance carriage 27 to be described below is provided in the presentexample embodiment.

FIG. 3A and FIG. 3B are provided to schematically illustrate aconfiguration of the maintenance carriage in accordance with the presentexample embodiment, and to be specific, FIG. 3A is a side view thereof,and FIG. 3B is a front view thereof.

The maintenance carriage 27 depicted in FIG. 3A and FIG. 3B includes acarriage base 29 configured to be supported and moved by multiplerollers 28 (wheels); a lift device 30 provided uprightly from thecarriage base 29; and a test head case 31 (case) that has a housingshape and accommodates the test head 15.

The carriage base 29 is provided with a handle 32, and the operator canmove the maintenance carriage 27 by pushing or pulling the handle 32.Each roller 28 is formed of a pair of wheels and configured to readilychange a direction, so that it is possible to improve the degree offreedom of movement of the maintenance carriage 27.

The lift device 30 includes a supporting column 33 extending from thecarriage base 29 toward an upper side in the drawing; a lifter 34provided at the supporting column 33 and configured to move along anextension direction of the supporting column 33, i.e., in the verticaldirection in the drawing; and a motor (not illustrated) configured tomove the lifter 34.

Further, each roller 28 of the carriage base 29 includes brake (notillustrated), and this brake is unlocked only when the lifter 34 ispositioned at the lowermost position in the vertical direction.

FIG. 4A and FIG. 4B schematically illustrate configurations of thelifter and the test head case of FIG. 3A and FIG. 3B, and to bespecific, FIG. 4A is a side view thereof, and FIG. 4B is a front viewthereof. For simple explanation, in FIG. 4A and FIG. 4B, the test head15 is indicated by dashed lines, and in FIG. 4B, a slide rail cover 40to be described later is indicated with a dashed dotted line and theslide rail cover 40 is illustrated in a see-through view.

As depicted in FIG. 4A and FIG. 4B, the test head case 31 has arectangular parallelepiped shape, and both ends of the test head case 31in a longitudinal direction are opened. When the test head 15 isunloaded from the cell 11, any one of the openings faces the maintenanceopening 26 of the cell 11. The unloaded test head 15 passes through themaintenance opening 26 and is accommodated within the test head case 31.Further, an upper portion of the test head case 31 is also opened.Therefore, the operator can access the test head 15 accommodated in thetest head case 31 through the open upper portion of the test head case31 and replace a main board through this upper portion.

The test head case 31 is supported by the lifter 34 via a horizontalposition adjusting stage 35. The horizontal position adjusting stage 35includes a base 35 a and a moving part 35 b, which are as circularplate-shaped members and are vertically overlapped. Between the base 35a and the moving part 35 b, multiple ball bearings (not illustrated) arearranged. Thus, the moving part 35 b can be horizontally moved on thebase 35 a. The base 35 a is connected with the lifter 34, and the movingpart 35 b is connected with the test head case 31. Therefore, thehorizontal position adjusting stage 35 can move the test head case 31horizontally with respect to the lifter 34.

Further, in the horizontal position adjusting stage 35, the moving part35 b can be fixed to the base 35 a by engaging a part of the base 35 awith a part of the moving part 35 b by supplying air from the outside.

Since the moving part 35 b is moved on the multiple ball bearings, greatstrength is not required to move the moving part 35 b. As a result, thetest head case 31 can be horizontally and easily moved by the operator.Further, a plate-shaped stopper 36 protrudes from a lower surface of thetest head case 31 toward the lower side, and when a horizontal movingamount of the test head case 31 reaches a preset level, the stopper 36is brought into contact with the base 35 a of the horizontal positionadjusting stage 35, so that the horizontal moving amount of the testhead case 31 can be regulated.

At both upper portions of side surfaces of the test head case 31 in thelongitudinal direction, there is provided a slide rail 37 formed ofmultiple balls. The slide rail 37 is configured to support the flange 17of the test head 15 accommodated in the test head case 31, and the testhead 15 is slid on the slide rail 37 in a longitudinal direction of thetest head case 31.

Further, at both ends of the upper portions of the side surface of thetest head case 31 in the longitudinal direction, there are providedstopper units 38 (fixing units). The stopper unit 38 includes aprotrudable protrusion-shaped contactor 39, and when the contactor 39protrudes to be brought into contact with the flange 17 of the test head15, a position of the test head 15 is fixed with respect to the testhead case 31. Further, in the lift device 30, when the test head 15 isaccommodated in the test head case 31, if the contactor 39 is notbrought into contact with the flange 17, the lifter 34 cannot bevertically moved.

When the test head 15 is slid in the longitudinal direction of the testhead case 31, the operator may be at risk of getting his/her hand,particularly finger, caught between the flange 17 and the slide rail 37.Therefore, the slide rail 37 is covered with the slide rail cover 40.

In the maintenance carriage 27, the lift device 30 can fix a position ofthe test head case 31 at a height where the slide rail 37 of the testhead case 31 directly faces the flange 17 of the test head 15accommodated within a first-level cell 11, a height where the same sliderail 37 directly faces the flange 17 of the test head 15 accommodatedwithin a second-level cell 11, a height where the same slide rail 37directly faces the flange 17 of the test head 15 accommodated within athird-level cell 11, and a height where the same slide rail 37 directlyfaces the flange 17 of the test head 15 accommodated within afourth-level cell 11.

Returning to FIG. 1, a guide rail 41 is provided at a lower portion ofthe outside of the cell tower 12. The guide rail 41 is provided alongthe longitudinal direction of the cell tower 12 and has a tube-shapedbody having a rectangular cross section. At a side wall 41 a of theguide rail 41 which is opposite to the cell tower 12, a slit 42 isformed. As depicted in FIG. 3B, the maintenance carriage 27 includesguide units 43 provided at the carriage base 29.

As depicted in FIG. 5, the guide unit 43 includes a bracket 43 aprotruding from the carriage base 29 toward an outside thereof; and aroller 43 b provided at a front end of the bracket 43 a and configuredto be horizontally rotated. The bracket 43 a enters into the guide rail41 through the slit 42 of the guide rail 41, and the roller 43 b isaccommodated within the guide rail 41. That is, the guide unit 43 is inthe movable fit with the guide rail 41, and in this case, the side wall41 a of the guide rail 41 is positioned between the roller 43 b and thecarriage base 29.

The above-described maintenance carriage 27 is used to unload the entireof the test head 15. In performing the maintenance of the test head 15,there may be no need to unload the entire of the test head 15. In thiscase, a simple maintenance carriage 44 configured to mount a part of thetest head 15 may be used instead of the maintenance carriage 27 in thewafer inspection apparatus 10.

FIG. 6A and FIG. 6B are side views schematically illustrating aconfiguration of a simple maintenance carriage, and to be specific, FIG.6A illustrates a case where maintenance is conducted to a test head of afirst-level cell in the cell tower, and FIG. 6B illustrates a case wheremaintenance is conducted to a test head of a second-level cell in thecell tower.

As depicted in FIG. 6A and FIG. 6B, the simple maintenance carriage 44includes a main frame 46 having multiple rollers 45 at a bottom portionthereof; and a maintenance table 47 configured to be vertically movedwith respect to the main frame 46. The maintenance table 47 includes aslide rail 48 formed of multiple balls, and the slide rail 48 isconfigured to support the flange 17 of the test head 15 of which a partis unloaded. The maintenance table 47 may be fixed at a first heightwhere the slide rail 48 directly faces the flange 17 of the test head 15accommodated within the first-level cell 11 and a second height wherethe slide rail 48 directly faces the flange 17 of the test head 15accommodated within the second-level cell 11.

The simple maintenance carriage 44 is greatly simplified and lightweightas compared with the maintenance carriage 27, and also includes themultiple rollers 45 provided at the bottom portion of the main frame 46.Thus, the operator can easily adjust a position of the simplemaintenance carriage 44, so that the slide rail 48 of the maintenancetable 47 can accurately face the flange 17 of the test head 15accommodated within the first-level or second-level cell 11. As aresult, it is possible to unload a part of the test head 15 from thefirst-level or second-level cell 11.

FIG. 7A to FIG. 7C are process diagrams for explaining a maintenancemethod for the wafer inspection apparatus with the maintenance carriageof FIG. 3A and FIG. 3B.

First, the rollers 43 b of the guide units 43 are inserted within theguide rail 41 at the end portion of the guide rail 41. Then, while therollers 43 b are inserted within the guide rail 41, the maintenancecarriage 27 is moved approximately to a position of the cell 11accommodating the test head 15 to be maintained. Thereafter, byoperating the brakes of the respective rollers 28 of the carriage base29, the maintenance carriage 27 is fixed at the position (FIG. 7A).

Then, the lift device 30 raises the test head case 31 to a height wherethe slide rail 37 of the test head case 31 directly faces the flange 17of the test head 15 to be maintained, and a position of the test headcase 31 is fixed (FIG. 7B).

Thereafter, the position of the test head case 31 is fine controlled inthe horizontal direction by the horizontal position adjusting stage 35in order for the slide rail 37 to accurately face the flange 17 of thetest head 15 to be maintained (FIG. 7C), and the present maintenancemethod is ended.

In the maintenance carriage 27 in accordance with the present exampleembodiment, the horizontal position adjusting stage 35 is providedbetween the lifter 34 of the lift device 30 arranged uprightly from themovable carriage base 29 and the test head case 31 configured toaccommodate the test head 15, and the test head case 31 is horizontallymoved with respect to the lifter 34 through the horizontal positionadjusting stage 35. Accordingly, the position of the carriage base 29 isfirst fixed. Then, the test head case 31 is moved up to the position ofthe test head 15 to be maintained, and the position of the test headcase 31 is fixed. Thereafter, the position of the test head case 31 canbe fine controlled in the horizontal direction such that the slide rail37 can accurately face the flange 17 of the test head 15 to bemaintained. As a result, it is possible to easily unload the test head15 toward the test head case 31.

In the above-described maintenance carriage 27, at the upper portions ofthe side surfaces of the test head case 31 in the longitudinaldirection, there is provided the slide rail 37 on which the test head 15is slid in the longitudinal direction of the test head case 31. Further,the slide rail 37 includes the stopper units 38 configured to fix theposition of the test head 15. Thus, the test head 15 accommodated withinthe test head case 31 can be moved to a desired position within the testhead case 31 and fixed at the position. Therefore, it is possible toimprove maintenance efficiency of the test head 15.

Further, the above-described maintenance carriage 27 further includesthe guide unit 43 which is in the movable fit with the guide rail 41provided at the lower side of the cell tower 12. Thus, the maintenancecarriage 27 can be accurately moved along the cell tower 12. Therefore,it is possible to reduce a time for adjusting the position of themaintenance carriage 27.

Furthermore, in the above-described maintenance carriage 27, the sidewall 41 a of the guide rail 41 is positioned between the carriage base29 and the roller 43 b provided at the front end of the bracket 43 aprotruding from the carriage base 29 toward the side direction thereof.Thus, even if the maintenance carriage 27 is tilted, since the roller 43b is engaged with the side wall 41 a of the guide rail 41, themaintenance carriage 27 can be suppressed from turning over.

Although the present disclosure has been explained with reference to theabove example embodiments, the present disclosure is not limitedthereto.

By way of example, the above-described maintenance carriage 27 isprovided only at the outside of the single cell tower 12. However, asdepicted in FIG. 8, two cell towers 12 may be arranged such thatoutsides thereof face each other, and the maintenance carriage 27 may beprovided between the two cell towers 12. In this case, the test headcase 31 of the maintenance carriage 27 has the openings at both ends inthe longitudinal direction, and each opening faces the maintenanceopening 26 of each cell 11 of the wafer inspection apparatus 10. Thus,all of the test heads 15 of the wafer inspection apparatus 10 can beaccommodated within the test head case 31. Therefore, it is possible toimprove maintenance efficiency of the test head 15.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims.

The claims of the present application are different and possibly, atleast in some aspects, broader in scope than the claims pursued in theparent application. To the extent any prior amendments orcharacterizations of the scope of any claim or cited document madeduring prosecution of the parent could be construed as a disclaimer ofany subject matter supported by the present disclosure, Applicantshereby rescind and retract such disclaimer. Accordingly, the referencespreviously presented in the parent applications may need to berevisited.

We claim:
 1. A wafer inspection system comprising: a transfer region in which a transfer device for transferring a wafer is arranged; a maintenance region in which a test head is maintained; a plurality of inspection rooms located between the transfer region and the maintenance region, and configured to receive and hold the test head within each of the plurality of inspection rooms, the test head being used when inspecting the wafer on which a semiconductor device is formed; and a maintenance carriage to support the test head arranged in the maintenance region, wherein the test head is unloaded onto the maintenance carriage from each of the plurality of inspection rooms.
 2. The wafer inspection system of claim 1, wherein the plurality of inspection rooms are arranged at multiple levels.
 3. The wafer inspection system of claim 1, wherein, in each of the plurality of inspection rooms, a first slide rail is provided to unload the test head onto the maintenance carriage from each of the plurality of inspection rooms.
 4. The wafer inspection system of claim 3, wherein the maintenance carriage has a second slide rail for supporting the test head unloaded onto the maintenance carriage from each of the plurality of inspection rooms.
 5. The wafer inspection system of claim 4, wherein the maintenance carriage has a lift device for positioning the second slide rail to a height directly facing the first slide rail. 